1. Field of the Invention
The present invention relates to a rack-driven power steering apparatus, and more particularly to a rack-driven power steering apparatus which mitigates frictional force and noise produced due to iron powder generated by continuous frictions while balls are circulating in inner peripheral screw grooves and outer peripheral screw groove defined by a rack bar and a ball nut, and collects iron powder scattered between the rack bar and the ball nut in one place so that the iron powder can be easily removed. Therefore, the rack-driven power steering apparatus can protect components, increase durability, and improve maintenance efficiency.
2. Description of the Prior Art
A general rack-driven power steering apparatus includes a steering system extending from a steering wheel to the two wheels, and an auxiliary power mechanism for supplying the steering system with auxiliary steering power.
FIG. 1 is a partially sectional view schematically illustrating a general rack-driven power steering apparatus. FIG. 2 is a sectional view schematically illustrating a belt type transmission unit of the general rack-driven power steering apparatus.
A general rack-driven power steering apparatus includes a steering system 100 extending from a steering wheel 105 to the two wheels 150, and an auxiliary power mechanism 160 for supplying the steering system with auxiliary steering power.
In the steering system 100, an upper end of a steering shaft 110 is connected to the steering wheel 105 to be rotated together with the steering wheel 105, and a lower end thereof is connected to a pinion shaft 120 by means of a pair of universal joints 115. The pinion shaft 120 is connected to the rack bar 155 through the rack-pinion mechanism 135, and opposite ends of the rack bar 155 are connected to the wheels 150 of the vehicle through a tie rod 140 and a knuckle arm 145.
The rack-pinion mechanism 135 is formed by engaging a pinion gear 125 formed at a lower end of the pinion shaft 120 with a rack gear 130 formed at one side of an outer peripheral surface of the rack bar 155.
The auxiliary power mechanism 160 includes a torque sensor 117 for detecting a steering torque applied to the steering wheel 105 by the driver and outputting an electrical signal proportional to the detected steering torque, an electronic control unit (ECU) for generating a control signal based on the electrical signal transmitted from the torque sensor 117, a motor 165 for generating an auxiliary steering power based on the control signal transmitted from the electronic control unit, and a belt type transmission unit 170 for transferring the auxiliary power generated by the motor 165 to the rack bar 155 by means of a belt 210.
The belt type transmission unit 170 includes a motor 165 controlled by the electronic control unit (ECU), a motor pulley 205a fixed to a shaft 165a of the motor 165, a belt 210 wound on the motor pulley 205a, a ball nut 220 installed within a rack housing 200 surrounding the rack bar 155 to support the rack bar 155, and a nut pulley 205b coupled to an outer peripheral surface of the ball nut 220.
The ball nut 220 is coupled to the rack bar 155 by means of balls to slide the rack bar 155 within the housing 200 while being rotated, and a bearing 240 for supporting rotation of the ball nut 220 is mounted to an outer peripheral surface of the ball nut 220.
However, according to the related art, iron powder is generated by continuous friction while the balls are circulating in an inner peripheral screw groove and an outer peripheral screw groove of the rack bar and the ball nut which increases frictional force and generates noise.
Further, the iron powder scattered between the rack bar and the ball nut lowers power transmission efficiency and disturbs accurate transmission of auxiliary power.
In addition, due to this, when an error or damage is severe in the ball nut, the nut pulley, the motor or the electronic control unit, steering may be disabled during high speed travel of the vehicle and thus a safety accident may be caused.